Can you help me?

1st off, u don't cuz the shoulders u cut the threads that hold the sleeve to the shirt. that keeps the fabric from shredding. it appears she cut all but the arm pit threads. the rest of this is a best guess...

leave roughly a half inch at the tuktok and bottom of the sleeve when you shred it. it looks like each piece is about 1/4-1/2 inch thick as well. use scissors carefully so you leave the half inch at the bottom and don't cut all the way through.

as for the neck, do the same thing only start just below the thicker part of the neck of the tee. I'd suggest turning the sando inside out and making the v shape with a marker so you know where to stop with the scissors. you also have to LEAVE THE SHOULDERS IN TACT!! if you cut the shoulder threads the sando falls apart. you can even see part of the right shoulder in the picture. i'd say leave 1/4-1/2 inch on either side of the shoulder stitching. it looks like she cut out the strips of fabric between the cuts, unlike in the sleeves. i'd guess she took out small strips and left those narrow ones you c.